Tebbe A W, Faulkner M J, Weiss W P
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691.
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691.
J Dairy Sci. 2017 Aug;100(8):6218-6228. doi: 10.3168/jds.2017-12719.
Many nutrition models rely on summative equations to estimate feed and diet energy concentrations. These models partition feed into nutrient fractions and multiply the fractions by their estimated true digestibility, and the digestible mass provided by each fraction is then summed and converted to an energy value. Nonfiber carbohydrate (NFC) is used in many models. Although it behaves as a nutritionally uniform fraction, it is a heterogeneous mixture of components. To reduce the heterogeneity, we partitioned NFC into starch and residual organic matter (ROM), which is calculated as 100 - CP - LCFA - ash - starch - NDF, where crude protein (CP), long-chain fatty acids (LCFA), ash, starch, and neutral detergent fiber (NDF) are a percentage of DM. However, the true digestibility of ROM is unknown, and because NDF is contaminated with both ash and CP, those components are subtracted twice. The effect of ash and CP contamination of NDF on in vivo digestibility of NDF and ROM was evaluated using data from 2 total-collection digestibility experiments using lactating dairy cows. Digestibility of NDF was greater when it was corrected for ash and CP than without correction. Conversely, ROM apparent digestibility decreased when NDF was corrected for contamination. Although correcting for contamination statistically increased NDF digestibility, the effect was small; the average increase was 3.4%. The decrease in ROM digestibility was 7.4%. True digestibility of ROM is needed to incorporate ROM into summative equations. Data from multiple digestibility experiments (38 diets) using dairy cows were collated, and ROM concentrations were regressed on concentration of digestible ROM (ROM was calculated without adjusting for ash and CP contamination). The estimated true digestibility coefficient of ROM was 0.96 (SE = 0.021), and metabolic fecal ROM was 3.43 g/100 g of dry matter intake (SE = 0.30). Using a smaller data set (7 diets), estimated true digestibility of ROM when calculated using NDF corrected for ash and CP contamination was 0.87 (SE = 0.025), and metabolic fecal ROM was 3.76 g/100 g (SE = 0.60). Regardless of NDF method, ROM exhibited nutritional uniformity. The ROM fraction also had lower errors associated with the estimated true digestibility and its metabolic fecal fraction than did NFC. Therefore, ROM may result in more accurate estimates of available energy if integrated into models.
许多营养模型依靠汇总方程来估算饲料和日粮的能量浓度。这些模型将饲料划分为营养成分，将各成分乘以其估计的真消化率，然后将各成分提供的可消化质量相加并换算为能量值。许多模型中使用了非纤维碳水化合物（NFC）。尽管它表现为营养成分均匀的部分，但实际上是多种成分的异质混合物。为了减少这种异质性，我们将NFC划分为淀粉和残余有机物（ROM），ROM的计算方法为100 - 粗蛋白（CP）- 长链脂肪酸（LCFA）- 灰分 - 淀粉 - 中性洗涤纤维（NDF），其中粗蛋白（CP）、长链脂肪酸（LCFA）、灰分、淀粉和中性洗涤纤维（NDF）均以占干物质（DM）的百分比表示。然而，ROM的真消化率未知，并且由于NDF同时受到灰分和CP的污染，这两种成分被重复减去。利用泌乳奶牛全收粪消化率实验的数据，评估了NDF的灰分和CP污染对NDF和ROM体内消化率的影响。校正灰分和CP后的NDF消化率高于未校正时。相反，校正NDF污染后，ROM的表观消化率下降。虽然校正污染在统计学上提高了NDF的消化率，但影响较小；平均提高了3.4%。ROM消化率的下降幅度为7.4%。要将ROM纳入汇总方程，需要知道其真消化率。整理了使用奶牛进行的多次消化率实验（38种日粮）的数据，并将ROM浓度对可消化ROM浓度进行回归分析（计算ROM时未对灰分和CP污染进行校正）。ROM的估计真消化率系数为0.96（标准误 = 0.021），代谢粪ROM为3.43克/100克干物质摄入量（标准误 = 0.30）。使用较小的数据集（7种日粮），当使用校正了灰分和CP污染的NDF计算时，ROM的估计真消化率为0.87（标准误 = 0.025），代谢粪ROM为3.76克/100克（标准误 = 0.60）。无论采用何种NDF方法，ROM都表现出营养均匀性。与NFC相比，ROM部分在估计真消化率及其代谢粪部分方面的误差也更低。因此，如果将ROM纳入模型，可能会更准确地估计可利用能量。
